This research project involves analysis of the nature of the morphogenetic field of the regenerating amphibian limb, and the mechanism whereby it respecifies new spatial patterns of cell differentiation. Work presently in progress includes (1) the mapping of the contribution of the four quadrants of the limb stump to the regeneration blastema, (2) determining whether the limb stump tissues impose anterior-posterior, dorsal-ventral or proximal-distal polarity on the undifferentiated blastema, and (3) determining whether distal outgrowth of the limb requires a complete set of transverse positional values at the blastema tip.